1. Field of the Invention
The present invention relates generally to magnetic tape cassettes and more particularly to a magnetic tape cassette suitable for use with a digital audio tape recorder.
2. Description of the Background
A digital audio tape recorder, which is now known as DAT, is now commercially available to permit the public to digitally record an analog signal, such as an acoustic signal, on a magnetic tape or to reproduce a digitally recorded signal therefrom. The digital audio tape recorder employs a rotary head to provide a recording format in which the digital signal is recorded with a relatively high data density, when compared with a stationary head.
In the magnetic tape cassette used in such high density recording, when the magnetic tape is smudged with fingerprints, oily compounds, dust or the like, a drop-out occurs in the reproduced signal. Therefore, the magnetic tape has to be sealed within the tape cassette as tightly as possible so that it can be protected from fingerprints, dust smudges, and the like.
A magnetic tape cassette shown in FIGS. 1 to 6 has previously been proposed for such a purpose, and Japanese Utility Model Laid-Open Gazette No. 1-017078 describes this kind of magnetic tape cassette.
FIG. 1 is a perspective view of a previously proposed magnetic tape cassette 1, in which a cassette housing shown generally at 2 comprises an upper half or part 3 and a lower half or part 4, which parts are secured together by conventional means, such as screws or the like (not shown). In lower part 4, as shown in FIG. 2, a pair of right and left reel shaft insertion apertures 5 are formed. A pair of reel hubs 7 are located within the cassette housing 2 and are rotatably inserted into the pair of reel shaft insertion apertures 5, and a magnetic tape 6 is wound around the pair of reel hubs 7. Magnetic tape 6 is guided by a pair of tape guide posts 8 formed at the left and right front corners of lower part 4, so that magnetic tape 6 is exposed along the front portion of cassette housing 2.
A pocket portion or cut-away area 10 is formed as a recess at the front surface of the lower part 4, corresponding to the location where magnetic tape 6 is exposed at the front surface of cassette housing 2. Pocket portion 10 is provided so that when magnetic tape cassette 1 is loaded into a digital audio tape recording and/or reproducing apparatus (now shown), and the front lid 12 is raised, a tape loading guide member of the apparatus can enter pocket portion 10 to pull the magnetic tape 6 out and around the rotary head drum in the tape loading operation.
A transparent window portion 11 is formed on upper part 3 of cassette housing 2, so that the user can visually confirm the amount of magnetic tape 6 wound around respective ones of the reel hubs 7.
Front lid 12 is rotatably supported on front end portions of upper part 3 of cassette housing 2 by two side plate portions 12a attached the two respective sides of cassette housing 2, so as to open and/or close the front of the cassette housing 2 where magnetic tape 6 is exposed. When magnetic tape cassette 1 is not in use, front lid 12 closes the front portion of cassette housing 2 where magnetic tape 6 is exposed, so that cassette housing 2 completely encloses and protects magnetic tape 6. At the time when magnetic tape cassette 1 is loaded into the digital audio tape recorder, the tape loading mechanism of the recorder rotates front lid 12 upwardly to expose magnetic tape 6.
A slidable plate member or slider 9 is movably mounted on the lower surface of lower part 4, so as to move slidably in the front to back direction of cassette housing 2. When magnetic tape cassette 1 is not in use, slider 9 is moved to it at the front closing position by action of a biasing spring 9', so that slider 9 closes the bottom of pocket portion 10, as well as closing the reel shaft insertion apertures 5 of lower part 4. When magnetic tape cassette 1 is loaded into the digital audio tape recorder, slider 9 is moved to the rear opening position by the tape loading mechanism of the apparatus, thereby opening pocket portion 10 and reel shaft insertion apertures 5.
Friction reducing sheets 20, 21 are provided on respective sides of the tape 6 as it is wound on reels 7 to cut down on friction between the housing 2 and the tape 6 as the tape is wound and unwound in the assembled cassette 1.
Further, cassette housing 2 incorporates therein a hub locking member 13 that is freely movable in the front to rear direction so as to interact with reel hubs 7 to avoid unnecessary rotation of reel hubs 7 when the cassette is not in use. This hub lock member 13 is comprised of a horizontal support plate portion 13a extending along an inner surface of upper part 3 in front of reel hubs 7 and side plate portions 13b extending downward from the ends of support plate portion 13a to form an upside-down, substantially U-shaped element when seen in front elevation. A pair of hub engaging elements 13c protrude from a rear edge of support plate portion 13a and are located to engage groove portions 7a of the two reel hubs 7. Two arm portions 13d project forward from the respective lower end portions of the side plate portions 13b, and engaging protrusions 13e are arranged at respective ends of arm portions 13d. These engaging protrusions 13e are provided to engage front lid 12, as will be described hereinbelow.
A torsion spring 14 is attached at a central portion of the support plate portion 13a of hub lock member 13, so that hub lock member 13 is always spring-biased in the locking direction by this torsion spring 14. More specifically, two end portions of torsion spring 14 extend outwardly to make contact with a front wall 3a of upper part 3, as shown in FIG. 3. Thus, hub lock member 13 is always spring-biased in the rearward direction, that is, in the direction in which engaging members 13c are engaged with engaging grooves 7a of reel hubs 7, so that when magnetic tape cassette 1 is not in use reel hubs 7 are locked against rotation. In this way, magnetic tape 6 is protected from being unwound and unduly slackened within the cassette. This reel locked state is shown in FIG. 5.
When magnetic tape cassette 1 is loaded into the digital audio tape recorder and front lid 12 is rotated upward as described above, the lower edges of side plate portions 12a of front lid 12 comes in contact with engaging portions 13e that extend outwardly at the two sides of hub lock member 13, whereby hub lick member 13 is moved in the direction so that engaging members 13c are disengaged from engaging grooves 7a of reel hubs 7, against the spring-biasing force of torsion spring 14. Thus, reel hubs 7 are released from the locked state and placed in a free-rotation state, which is shown in FIG. 6.
When magnetic tape cassette 1 having the above-described hub lock member 13 is assembled, hub lock member 13 is mounted in advance on upper part 3, before upper part 3 and lower part 4 are fastened together. That is, hub lock member 13 is initially fastened to upper part 3 and, so that at the time upper part 3 and lower part 4 are fastened together, hub lock member 13 is incorporated within the assembly of cassette housing 2.
More particularly, in the structure used for temporarily assembling hub lock member 13 to upper part 3, fixed pins 15 project downwardly from an inner surface of upper part 3 in the vicinity of cut-away portion 10. In correspondence therewith two, engaging, convex, open portions 16 are formed on the front edge of support portion 13a of hub lock member 13. Therefore, when hub lock member 13 is moved outside of its normal movable range, that is, when hub lock member 13 is moved ahead of the lock releasing position where front lid 12 is opened to the maximum, engaging concave portions 16 are engaged with fixed pins 15, whereby hub lock member 13 is temporarily fastened to upper part 3. The diameters of fixed pins 15 and the size of the open portions 16 are selected so that lock member 13 can be attached to upper part 3 by applying only a small pressure.
Thus, when upper part 3 having hub lock member 13 temporarily secured thereto is combined with lower part 4, in which magnetic tape 6, reels 7 and the like have been partly assembled, the overall magnetic tape cassette can be assembled with ease.
Once the magnetic tape cassette has been assembled as described above and hub lock member 13 is temporarily fastened to pins 15 of upper part 3, as shown in FIG. 4, the ends of arm portions 13d of hub lock member 13 can be pushed rearwardly and the engagement between engaging concave portions 16 and fixed pins 15 is released, thereby permitting hub lock member 13 to become movable. The releasing of engagement between portions 16 and pins 15 can be done manually or by the cassette assembly machine.
When front lid 12 is closed during nonuse of the magnetic tape cassette, as shown in FIG. 5, hub lock member 13 locks reel hub 7 by engaging protruding elements 13c with engaging slit portions 7a of reel hubs 7, in the rearmost movable position of hub lock member 13 under action of spring 14. When front lid 12 is rotated in its opening direction upon use of the magnetic tape cassette, as shown in FIG. 6, hub lock member 13 is simultaneously moved forward so that protruding elements 13c of hub lock members 13 are disengaged from engaging slit portions 7a, thereby releasing reel hubs 7 from the locked condition.
When hub lock member 13 is moved in consort with the opening and closing of front lid 12, hub lock member 13 is generally precluded from once again being temporarily fastened to upper part 3. More specifically, engaging concave portions 16 are engaged with fixed pins 15 generally only when hub lock member 13 has been moved to a position that is ahead of the normal reel hub lock releasing position. Thus, even though hub lock member 13 is moved in consort with the opening and closing of front lid 12 in a predetermined range, engaging concave portions 16 can be prevented from being engaged with fixed pins 15 by keeping the distance therebetween outside of that predetermined range of movement.
The above-described structure for temporarily fastening the hub lock member is described in Japanese Utility Model Application 62-199244 assigned to the assignee hereof.
Nevertheless, the magnetic tape cassette having the above-mentioned hub lick member temporary fastening structure has the unavoidable disadvantage that although hub lock member 13 can be prevented from being once again temporarily fastened to upper part 3 in the normal movement of hub lock member 13 in consort with the opening and closing of front lid 12, if the magnetic tape cassette is inadvertently dropped there is then the substantial possibility that hub lock member 13 will be once again temporarily fastened to upper part 3.
More specifically, when cassette housing 2 receives a considerable mechanical shock hub lock member 13 can be accidentally moved beyond its normal range so that engaging concave portions 16 can again be engaged with fixed pins 15, that is, the temporarily fastened state shown in FIG. 4 is revisited. As a result, during nonuse of the magnetic tape cassette and after such mechanical shock, the magnetic tape cassette is in the condition that the reel hubs 7 are released from being locked, so that magnetic tape 6 can become unduly slackened, thereby rendering hub lock member 13 generally useless.